A jack-up rig is an offshore oil and gas exploration or production drilling structure or a work-over platform being used in shallow water, typically in water with depths up to 500 feet. The jack-up rig usually comprises a floatable hull with a deck or working platform, and three or four legs, where the legs provide support for the floatable hull in elevated conditions. After the jack-up rig arrives on location, the legs are lowered until they touch the underneath seabed and rest on the soil at the seabed; then the hull may be jacked up using a jacking system to raise the working platform above the water, making the jack-up rig safe to be operated in open water situations where water movement is experienced.
During drilling operation, the oil or gas is drilled in an under seabed reservoir by drilling equipment on the working platform of a Jack-up rig; the drilling is usually through a riser. The existing options for providing protections to a riser include:
1. Drilling with the riser unprotected,
2. Providing coatings to the riser to protect against corrosion, fouling etc, but without protection from large ice or ship impacts.
3. Drilling through a minimal wellhead platform which supports the wellhead and conductor but is not designed to provide protection from large forces, for example ice or ship impacts.
4. Drilling through a substantial protection structure such as a conical piled monopod (CPM).
5. Drilling form a large combined drilling and production platform.
Options 3, 4 and 5 are all permanent structures and cannot be easily removed for reuse when the drilling activity is complete and not economical for exploration drilling where only one well is drilled at a location. As they are permanent they must also be designed for the worst possible design conditions as they cannot be removed if unusually large forces are expected.